1. Field of the Invention
The present invention relates to novel polyamide-based compositions which have been rendered fireproof by incorporation of red phosphorus therein, and to the use of such compositions in the fabrication of shaped articles well suited for electrical and electronic applications.
2. Description of the Prior Art
It is known to this art that the addition of red phosphorus to compositions based on polyamides imparts a high degree of fire resistance to same. However, the use of red phosphorus has a serious disadvantage in that it gives rise to the evolution of highly toxic hydrogen phosphide, which is formed under the action of the trace amounts of water present in the polymer and of the high temperature necessary for its conversion. It is also known that this disadvantage can be essentially overcome by the incorporation into the fireproof compositions of certain substances, such as metal compounds, which serve to fix the hydrogen phosphide. U.S. Pat. No. 3,883,475 features the use of cupric oxide for such purpose. French Pat. No. 2,367,100 describes an improvement wherein cadmium oxide is used in place of the CuO; in addition to its efficacy (at least equal to that of CuO) in inhibiting the evolution of phosphine, cadmium oxide also enables production of shaped articles having an especially high arc tracking resistance (in terms of French Standard Specification No. C 26220), which is equal to or greater than 400 volts in the case of compositions devoid of filler material and 375 volts in the case of compositions containing more than 25% by weight of fibrous glass filler.
The aforesaid '100 French patent also describes an additional improvement in the results obtained using cadmium oxide, and which features coating the red phosphorus with a polymeric material.
However, the cadmium oxide used in the fireproofed compositions of the prior art presents a practical problem associated with the known toxicity of this oxide, which no doubt strongly militates against the widespread use thereof.